This invention relates to an intermetallic compound-based, composite superconductor, and more particularly to an intermetallic compound-based, composite superconductor suitable for use in superconducting coils, etc. for generating a high magnetic field, where the superconductive part is formed by a thermal diffusion reaction.
Superconducting coils for use in a nuclear fusion reactor utilize an intermetallic compound-based superconductor having distinguished high magnetic field characteristics as a conductor owing to the necessity for generating a high magnetic field. According to the most popular structure of an intermetallic compound-based composite superconducting wire member, a large number of filaments are evenly distributed and contained in a matrix. The filaments contain a superconductive compound formed by diffusion reaction of the element in the filaments with the element in the matrix through a high temperature heat treatment, such as niobium-tin (Nb.sub.3 Sn), etc., and diffusion barriers are provided around the matrix to prevent a portion of the superconductive compound-forming element in the matrix from diffusion into a stabilizer during the thermal diffusion reaction.
According to other examples of intermetallic compound-based, composite superconducting wire members having different structures from the above-mentioned one, a single diffusion barrier is provided in the stabilizer, or the individual filaments are surrounded by independent diffusion barriers, respectively. The individual intermetallic compound-base, composite superconducting wire members given above are used in coils for a relatively small electric current.
On the other hand, the necessary superconductor for use in superconducting coils for a nuclear fusion reactor is a conductor for generating a high magnetic field and carrying a large electric current such as more than 10 KA and more than 10 T, and thus it is composed from a plurality of the above-mentioned intermetallic compound-based, composite superconducting wire members.
Generally, a conductor for a high magnetic field and a large electric current comprises a plurality of the above-mentioned intermetallic compound-based, composite superconducting wire members which are stranded and which are provided in a conduit made from a high strength structural material, where a coolant passes through interstices between the plurality of the stranded wire members in the conduit to cool the conductor. Since the conductor for a high magnetic field and a large electric current is in a structure that a plurality of intermetallic compound-based, composite superconducting wire members are stranded and encased in a conduit, a large AC loss is generated by the coupling currents induced between the intermetallic compound-based, composite superconducting wire members.
The conventional alloy-based, composite superconducting wire member, for example, a NbTi-based composite superconducting wire member, requires no high temperature heat treatment, and thus the AC loss can be suppressed by applying an organic insulation to the surface of the wire member, whereas a conductor for a high magnetic field and a large electric current composed from a compound-based composite superconducting wire member requires a high temperature heat treatment, and thus it is hard to apply the organic insulation to the surface of the wire member. That is, there is such a disadvantage that the AC loss cannot be reduced.
Intermetallic compound-based, composite superconducting wire members, where the superconductive part is formed by heat treatment, are disclosed in Japanese patent applications Kokai (Laid-open) Nos. 59-191208 and 59-191213.